A cover for a drainage device, in particular a drainage channel with a channel body such that the cover can be set on an upper edge of the channel body, which comprises detent ridges that extend into the channel body and which has at least one fixing element to attach the cover to the channel body or to a frame disposed on the channel body to reinforce its upper edge, such that in a locked state the fixing element engages a recess in the channel body or frame. In order to achieve durable fixation of the cover on the channel body, while enabling the fixing element to be simple to manufacture and install, and the channel cross-section to remain free, the detent ridges comprise at least one aperture to guide the fixing element, which projects out of that aperture.